Uniffi based bindings for the Rust SDK crypto crate
This crate contains Uniffi based bindings for the matrix-sdk-crypto crate. The
README mainly describes how to build and integrate the bindings into a Kotlin
based Android project, but the Android specific bits can be skipped if you are
targeting an x86 Linux project.
To build and distribute bindings for iOS projects, see a dedicated page
Prerequisites
Rust
To build the bindings Rust will be needed it can be either installed using an OS specific package manager or directly with the provided installer.
Android NDK
The Android NDK will be required as well, it can be installed either through Android Studio or directly using an installer.
Configuring Rust for cross compilation
First we'll need to install the Rust target for our desired Android architecture, for example:
# rustup target add aarch64-linux-android
This will add support to cross-compile for the aarch64-linux-android target, Rust supports many different targets, you'll have to make sure to pick the right one for your device or emulator.
After this is done, we'll have to configure Cargo to use the correct linker for our target, by providing the Cargo setting of target..linker with a value of the path to an appropriate linker in your NDK installation.
This may be set through an environment variable:
$ export CARGO_TARGET_AARCH64_LINUX_ANDROID_LINKER="<path-to-ndk-installation>/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android30-clang"
Alternatively, it may be set in the .cargo/config.toml file in the current
directory, any parent directory, or your home directory:
[target.aarch64-linux-android]
linker = "<path-to-ndk-installation>/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android30-clang"
Building
To enable cross compilation for olm-sys which builds our libolm C library
we'll need to set the ANDROID_NDK environment variable to the location of our
Android NDK installation.
$ export ANDROID_NDK=$HOME/Android/Sdk/ndk/<some-installed-version>
Also, include the NDK tools directory in your PATH:
$ export PATH="$ANDROID_NDK/toolchains/llvm/prebuilt/linux-x86_64/bin:$PATH"
Building for a target
The bindings can built for the aarch64 target with:
$ cargo build --target aarch64-linux-android
After that, a dynamic library can be found in the
target/aarch64-linux-android/debug directory, under the repository root
directory. The library will be called libmatrix_sdk_crypto_ffi.so and needs to
be renamed and copied into the jniLibs directory of your Android project, for
Element Android:
$ cp ../../target/aarch64-linux-android/debug/libmatrix_sdk_crypto_ffi.so \
/home/example/matrix-sdk-android/src/main/jniLibs/aarch64/libuniffi_olm.so